Revised Julian Calendar

The Revised Julian Calendar is a calendar that was considered for adoption by several Orthodox churches at a synod in Constantinople in May 1923. The synod synchronized the new calendar with the Gregorian Calendar by specifying that October 1, 1923, in the Julian Calendar will be October 14 in the Revised Julian Calendar, thus dropping thirteen days. It then adopted a leap year rule that differs from that of the Gregorian calendar: Years evenly divisible by four are leap years, except that years evenly divisible by 100 are not leap years, unless they leave a remainder of 200 or 600 when divided by 900, in which case they are leap years. This means that the two calendars will first differ in 2800, which will be a leap year in the Gregorian Calendar, but a common year in the Revised Julian Calendar. This leap year rule was proposed by Milutin Milankovic, an astronomical delegate to the synod representing the governments of the Serbs, Croatians, and Slovenes.

Milankovic selected this rule, which produces an average year length of 365.242222… days, because it was within two seconds of the then current length of the mean tropical year. However, the vernal equinox year is slightly longer, so for a few thousand years the Revised Julian Calendar doesn't do as good a job as the Gregorian Calendar at keeping the vernal equinox on or close to March 21. But the length of a day is increasing by about 1.7 milliseconds per century (due to tidal acceleration), so the number of days per year decreases by about 0.0001 each millennium. This means that in the long run, the Revised Julian Calendar will also be inaccurate even if the mean tropical year is the basis.

The synod also adopted an astronomical rule for Pascha: Pascha is the Sunday after the midnight-to-midnight day at the meridian of the Church of the Holy Sepulchre in Jerusalem during which the first full moon after the vernal equinox occurs. Although the instant of the full moon must occur after the instant of the vernal equinox, it may occur on the same day. If the full moon occurs on a Sunday, Easter is the following Sunday. However, all Orthodox churches rejected this rule and continue to use the Julian Calendar to determine the date of Pascha (except for the Churches of Finland and Estonia, which use the Gregorian Paschalion).

Conversion from Old Style to New Style

Sometimes confusion can result when converting dates from one calendar to another if the dates are shifted rigidly by 13 days. Since it must be assumed that the two calendars run parallel to one another, any particular "day" will have two "dates." Like wise a single "date" in the respective calendars will represent two different "days."

For example: John (Maximovitch) of Shanghai and San Francisco (1896 - 1966) died on Jun 19 J / Jul 2 G when the deviation between the Julian and Gregorian calendars was 13 days, as it is at the time of this writing. Therefore, he should be commemorated on the same "day," but on a different "date" in the two respective calendars. He should not be commemorated on June 19 G as is common, a date which corresponds to the June 19 RJ, which would imply that he reposed on Jun 6 J, which is untrue from the perspective of any calendar.

Another example: It is sometimes remarked that William Shakespeare and Miguel de Cervantes died on the same date, 23 April 1616, but not on the same day. England was still using the Julian calendar in 1616, while Spain was using the Gregorian calendar. Cervantes actually died ten days before Shakespeare. Therefore: Cervantes + Apr 13 J / Apr 23 G & Shakespeare + Apr 23 J / May 3 G.

Another example: George Washington (1789-1797) was born on February 11 J, before 1753 when America changed over. In his times the difference between the old and new calendars was 11 days. That is why his birthday is celebrated on February 22 G. Americans do not celebrate his birthday on Feb 11 G. Rather we celebrate it on Feb 22 G, the equivalent of Feb 11 J.

The proper conversion would perhaps require taking into account how much deviation between the two calendars had occurred at the time of the event being commemorated. The following table shows the amount of deviation between the Julian and Gregorian calendars. Conversion between the Julian and Revised Julian is more complex.

1–100 -2

100–200 -1

200–300 0

300–500 +1

500–600 +2

600–700 +3

700–900 +4

900–1000 +5

1000–1100 +6

1100–1300 +7

1300–1400 +8

1400–1500 +9

1500–1700 +10

1700–1800 +11

1800–1900 +12

1900–2100 +13

2100–2200 +14

2200–2300 +15

2300–2500 +16

2500–2600 +17 etc...

note: time period is from from March 1 of first year to February 29 of last year.

Reference

Miriam Nancy Shields, "The new calendar of the Eastern churches", Popular Astronomy 32 (1924) 407-411. This is a translation of M. Milankovitch, "The end of the Julian calendar and the new calendar of the Eastern churches", Astronomische Nachrichten No. 5279 (1924).[1]